Regeneration method for a particulate filter

ABSTRACT

A method for regenerating a particulate filter of an internal combustion engine. The method includes passing an exhaust gas stream through the particulate filter, determining what kind of fuel is being combusted in the internal combustion engine, and determining a burn-off temperature that is capable of burning off a kind of soot formed in the particulate filter as a result of the combustion of the kind of fuel. The burn-off temperature is based on the kind of fuel.

FIELD OF THE DISCLOSURE

The present disclosure relates to a regeneration method for a particulate filter.

BACKGROUND OF THE DISCLOSURE

Some combustion engines allow a secondary injection of fuel in a fourth stroke (i.e., the exhaust stroke), and in such engines, the fuel remaining in the exhaust gas stream, as a result of incomplete combustion, may be oxidized in an oxidation catalyst positioned upstream of the particulate filter. In some other engines, a secondary injection of fuel outside of the diesel engine may occur in a section of the exhaust gas tract positioned upstream of the oxidation catalyst. Secondary injections lead to a corresponding increases in the exhaust gas stream temperatures, and such an increase may be used to regenerate the particulate filter.

The energy content of biofuel is lower than that of diesel fuel. And because of this energy difference, a quantity of the secondary injection may need to vary, so as to ensure that the correct exhaust gas stream temperatures are reached and that regeneration of the particulate filter can occur. At the same time, the quantity of the secondary injection may need to be kept to a minimum, so as to improve the overall fuel efficiency of the engine.

SUMMARY OF THE DISCLOSURE

Disclosed is a method for regenerating a particulate filter of an internal combustion engine. The method includes passing an exhaust gas stream through the particulate filter, determining what kind of fuel is being combusted in the internal combustion engine, and determining a burn-off temperature that is capable of burning off a kind of soot formed in the particulate filter as a result of the combustion of the kind of fuel. The burn-off temperature is based on the kind of fuel. Such a method ensures that the correct exhaust gas stream temperature is reached, so that regeneration of the particulate filter may occur. Additionally, such a method may simultaneously ensure that the quantity of the secondary injection is minimized, so as to improve the fuel efficiency of the diesel engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description of the drawings refers to the accompanying figures in which:

FIG. 1 is a flow chart of a method for regenerating a particulate filter, and

FIG. 2 is a diagrammatic illustration of an aftertreatment system that may utilize the method illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1-2, there is shown a method for regenerating a particulate filter 18. Upon startup of a vehicle, step 100 initiates an electronic control unit (“ECU”) 10, the ECU 10 being part of an upper level engine control unit 24, in at least some embodiments. Exhaust gas flows from an internal combustion engine 14 of the vehicle and through an aftertreatment system 12, which includes an oxidation catalyst 16 and the particulate filter 18 downstream thereof. The exhaust gas flows out of the particulate filter 18, out of an exhaust system 20, and ultimately, out into the outside environment.

Although not shown in the FIGS., some embodiments of the aftertreatment system 12 may include a selective catalytic reduction (“SCR”) catalyst positioned downstream of the particulate filter 18, but upstream of a final portion the exhaust system 20. In such embodiments, a urea doser 22 may inject a urea solution, such as AdBlue or DEF, upstream of the SCR catalyst and into the exhaust gas stream, the urea solution being used for reducing a NO_(x) content of the exhaust gas flowing out of the exhaust system 20. The ECU 10 may control the urea doser 22.

In step 101, the ECU 10 determines what kind of fuel is being used by the engine 14, some examples of which include diesel fuel, biofuel, and a blend of diesel fuel and biofuel. The viscosity, the dielectric conductivity, and/or the density of the fuel—all being indicative of the kind of fuel—may be determined as a result of determining a fuel temperature via a temperature sensor 28, for example. Alternatively, these same properties may be determined by evaluating the oscillation or sound propagation behavior of the fuel via a fuel sensor 26. In such embodiments, the fuel sensor 26 may be one that is produced by Measurement Specialties Inc. (e.g., sensor FPS28xx that utilizes a tunable quartz resonance fork). Other embodiments of the disclosed method for regenerating the particulate filter 18 may use various other kinds of sensors, one such example being a high-resolution pressure sensor.

The fuel sensor 26 and the temperature sensor 28 may both be positioned in a fuel tank 30, so that they are continuously exposed to the fuel therein. Both the fuel sensor 26 and the temperature sensor 28 provide signals to the ECU 10, and then, the ECU 10 may establish a relationship between the signals and the kind of fuel by using characteristic maps, for example.

In step 102, the ECU 10 estimates the instantaneous charging state (η) of the particulate filter 18, the instantaneous charging state (η) being the amount of soot in the particulate filter 18 at a given time. Among other things, this estimation is based on the kind of fuel that is determined in step 101. For example, the estimation may factor in that fossil fuels, such as diesel fuel, form soot on the particulate filter 18 more quickly than biofuels do.

Further, in step 102, the ECU 10 may estimate the charging state (η) based on the loads on the engine 14. The utilization level of the engine 14 (e.g., a low overall power utilization or a high overall power utilization) may also be used for estimating the charging state (η) of the particulate filter 18. Low loads and low power utilization of the engine 14 may result in slower soot formation on the particulate filter 18 than, for example, a high loads and high power utilization. The load-related engine parameters are determined for a predetermined measurement duration, the duration being a period of time between the current time and the time of the last regeneration.

Still further, in step 102, the ECU 10 may estimate the instantaneous charging state (η) based on a lambda value (λ). The lambda value (λ) represents the air-fuel ratio, and may be determined using, for example, a lambda sensor 32 positioned in the exhaust gas stream. The lambda value (λ) being less than one represents a rich mixture and is indicative of increased soot formation, but decreased NO_(x) formation. In contrast, the lambda value (λ) being greater than one represents a lean mixture and is indicative of decreased soot formation, but increased NO_(x) formation.

As shown in step 103, there may be several regeneration triggers. As a first example, if the ECU 10 determines that the instantaneous charging state (η) exceeds a predetermined limit value (ηlimit), then the ECU 10 triggers a beginning of a regeneration process in step 104. The regeneration process occurs at a burn-off temperature (Treg), which is a temperature capable of burning off the kind of soot formed in the particulate filter 18 as a result of the combustion of the kind of fuel. The burn-off temperature (Treg) varies relative to the kind of fuel being used in the engine 14. For example, the burning of soot originating from the biofuels requires a lower burn-off temperature (Treg) than the burning of soot originating from fossil fuels, such as diesel fuel. The burn-off temperature (Treg) may be based on empirically determined relationships that are stored in the ECU 10 (i.e., temperature maps).

Further, a second regeneration trigger in step 103 may be the operating time (τ) of the particulate filter 18 that has elapsed since the last regeneration process was performed. For example, the regeneration trigger may occur when the operating time (τ) of the particulate filter 18 is greater than an operating time limit (τlimit), the operating time limit (τlimit) being somewhere between 10 and 100 hours, in at least some embodiments.

Still further, a third regeneration trigger in step 103 may be the pressure difference (Δp) between an inlet and an outlet of the particulate filter 18, as determined by pressure sensors 34 and 36. To illustrate, if the pressure difference exceeds a characteristic maximum value (plimit), then there is a high probability that there is an excessive charging state (η) of the particulate filter 18. Ultimately, in step 103, the ECU 10 may begin regenerating the particulate filter 18 as soon as any of the three regeneration triggers occur. And alternatively, if none of the three regeneration criteria occur, then the regeneration process returns to step 101.

The engine 14 may allow a secondary injection of fuel in a fourth stroke (i.e., the exhaust stroke). And in such an engine 14, the fuel remaining in the exhaust gas stream, as a result of incomplete combustion, may be oxidized in the oxidation catalyst 16 that is positioned upstream of the particulate filter 18. In an alternative embodiment of the engine 14, a secondary injection of fuel outside of the engine 14 may occur in a section of the exhaust gas tract positioned upstream of the oxidation catalyst 16. Secondary injections lead to increases in the exhaust gas stream temperatures, and such an increase may be used to regenerate the particulate filter 18. In either case, a secondary injection quantity (k) needs to be enough to regenerate the particulate filter 18, but simultaneously low enough to keep the secondary injection quantity (k) to a minimum, so as to improve the fuel efficiency of the diesel engine.

In step 104, the ECU 10 determines the burn-off temperature (Treg) and the associated secondary injection quantity (k). The burn-off temperature (Treg) is high enough, so as to affect the exhaust gas stream temperature that is in contact with the oxidation catalyst 16. Because the energy value of biofuels is lower than that of fossil diesel fuels, a relatively higher secondary injection quantity (k) is required for reaching the same exhaust gas stream temperature or burn-off temperature (Treg). Compliance with the burn-off temperature (Treg) may be monitored by a temperature control included in the aftertreatment system 12. For example, in the illustrated embodiment, the temperature control includes temperature sensors 38, 40, and 42 in an arrangement distributed over an inlet of the oxidation catalyst 16 and both the inlet and the outlet of the particulate filter 18, respectively. The temperature sensors 38, 40, and 42 provide temperature signals to the ECU 10. The temperature sensors 40, 42 may be used for regulating the secondary injection quantity (k), ensuring that the predetermined burn-off temperature (Treg) is reached at all locations within the particulate filter 18. This may ensure complete and consistent regeneration of the particulate filter 18.

The regeneration process may occur for a fixed period time (e.g., 20 to 30 minutes), and after the elapse of this span of time, the regeneration process is terminated in step 105.

While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. It will be noted that alternative embodiments of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the present invention as defined by the appended claims. 

1.-8. (canceled)
 9. A method for regenerating a particulate filter of an internal combustion engine, the method comprising: passing an exhaust gas stream through the particulate filter; determining what kind of fuel is being combusted in the internal combustion engine; and determining a burn-off temperature that is capable of burning off a kind of soot formed in the particulate filter as a result of the combustion of the kind of fuel, the burn-off temperature being based on the kind of fuel.
 10. The method of claim 1, wherein the burn-off temperature is a base burn-off temperature, the base burn-off temperature being a lowest temperature capable of burning off the kind of soot formed in the particulate filter as a result of the combustion of the kind of fuel.
 11. The method of claim 1, wherein the kind of fuel is a blend of a diesel fuel and a biofuel.
 12. The method of claim 1, comprising the step of regenerating the particulate filter at the burn-off temperature.
 13. The method of claim 1, comprising the step of determining an instantaneous charging state of the particulate filter based on the step of determining the kind of fuel, the instantaneous charging state being an amount of soot in the particulate filter at a given time as a result of the combustion of the kind of fuel.
 14. The method of claim 13, comprising the step of regenerating the particulate filter at the burn-off temperature when the instantaneous charging state of the particulate filter exceeds a predetermined limit value, the predetermined limit value being a limit of an amount of soot that can be contained in the particulate filter.
 15. The method of claim 14, wherein the burn-off temperature is a base burn-off temperature, the base burn-off temperature being a lowest temperature adequate to burn-off the kind of soot formed in the particulate filter as a result of the combustion of the kind of fuel.
 16. The method of claim 14, wherein the step of regenerating the particulate filter at the burn-off temperature comprises injecting one or more secondary injections of the kind of fuel, an overall flow of the one or more secondary injections is based on the kind of fuel, and the overall flow is high enough to reach the burn-off temperature.
 17. The method of claim 16, wherein the overall flow of the one or more secondary injections is not high enough to substantially exceed the burn-off temperature.
 18. The method of claim 17, wherein the burn-off temperature is a base burn-off temperature, the base burn-off temperature being a lowest temperature capable of burning off the kind of soot formed in the particulate filter as a result of combustion of the kind of fuel.
 19. The method of claim 14, wherein the step of regenerating the particulate filter at the burn-off temperature comprises injecting one or more secondary injections of the kind of fuel, an overall length of time of the step of regenerating the particulate filter is based on the kind of fuel, and an overall length of time of each of the one or more secondary injections is long enough to reach the burn-off temperature.
 20. The method of claim 19, wherein the overall length of time of the each of the one or more secondary injections is not long enough to substantially exceed the burn-off temperature.
 21. The method of claim 9, wherein the step of determining the kind of fuel comprises determining a viscosity of the kind of fuel.
 22. The method of claim 21, wherein the step of determining the viscosity of the kind of fuel comprises determining a temperature of the kind of fuel.
 23. The method of claim 21, wherein the step of determining the viscosity of the kind of fuel comprises evaluating a sound propagation behavior of the kind of fuel.
 24. The method of claim 9, wherein the step of determining the kind of fuel comprises determining a dielectric conductivity of the kind of fuel.
 25. The method of claim 24, wherein the step of determining the dielectric conductivity of the kind of fuel comprises determining a temperature of the kind of fuel.
 26. The method of claim 24, wherein the step of determining the dielectric conductivity of the kind of fuel comprises evaluating a sound propagation behavior of the kind of fuel.
 27. The method of claim 9, wherein the step of determining the kind of fuel comprises determining a density of the kind of fuel.
 28. The method of claim 27, wherein the step of determining the density of the kind of fuel comprises determining a temperature of the kind of fuel. 